Commit-ID: 0c96b27305faf06c068b45e07d28336c80dac286
Gitweb: http://git.kernel.org/tip/0c96b27305faf06c068b45e07d28336c80dac286
Author: Ethan Barnes <Ethan.Barnes@xxxxxxx>
AuthorDate: Wed, 19 Jul 2017 22:36:00 +0000
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Thu, 20 Jul 2017 16:40:24 +0200
smp/hotplug: Handle removal correctly in cpuhp_store_callbacks()
If cpuhp_store_callbacks() is called for CPUHP_AP_ONLINE_DYN or
CPUHP_BP_PREPARE_DYN, which are the indicators for dynamically allocated
states, then cpuhp_store_callbacks() allocates a new dynamic state. The
first allocation in each range returns CPUHP_AP_ONLINE_DYN or
CPUHP_BP_PREPARE_DYN.
If cpuhp_remove_state() is invoked for one of these states, then there is
no protection against the allocation mechanism. So the removal, which
should clear the callbacks and the name, gets a new state assigned and
clears that one.
As a consequence the state which should be cleared stays initialized. A
consecutive CPU hotplug operation dereferences the state callbacks and
accesses either freed or reused memory, resulting in crashes.
Add a protection against this by checking the name argument for NULL. If
it's NULL it's a removal. If not, it's an allocation.
[ tglx: Added a comment and massaged changelog ]
Fixes: 5b7aa87e0482 ("cpu/hotplug: Implement setup/removal interface")
Signed-off-by: Ethan Barnes <ethan.barnes@xxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxx>
Cc: "Srivatsa S. Bhat" <srivatsa@xxxxxxx>
Cc: Sebastian Siewior <bigeasy@linutronix.d>
Cc: Paul McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/DM2PR04MB398242FC7776D603D9F99C894A60@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
---
kernel/cpu.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index eee0331..a88c29a 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1252,7 +1252,17 @@ static int cpuhp_store_callbacks(enum cpuhp_state state, const char *name,
struct cpuhp_step *sp;
int ret = 0;
- if (state == CPUHP_AP_ONLINE_DYN || state == CPUHP_BP_PREPARE_DYN) {
+ /*
+ * If name is NULL, then the state gets removed.
+ *
+ * CPUHP_AP_ONLINE_DYN and CPUHP_BP_PREPARE_DYN are handed out on
+ * the first allocation from these dynamic ranges, so the removal
+ * would trigger a new allocation and clear the wrong (already
+ * empty) state, leaving the callbacks of the to be cleared state
+ * dangling, which causes wreckage on the next hotplug operation.
+ */
+ if (name && (state == CPUHP_AP_ONLINE_DYN ||
+ state == CPUHP_BP_PREPARE_DYN)) {
ret = cpuhp_reserve_state(state);
if (ret < 0)
return ret;
--
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